1. Field of the Invention
The present invention relates to an image forming apparatus such as a sheet transfer apparatus, a multifunction peripheral such as an electrophotographic multifunction peripheral having the sheet transfer apparatus, a facsimile machine, a printer such as a laser printer, a printing machine such as a stencil printing machine, an inkjet recording apparatus, or a multifunction peripheral formed of a combination of at least two of these apparatuses, and the like.
2. Description of the Related Art
There has been a growing need for downsizing image forming apparatuses such as multifunction peripherals including PPCs (Plain Paper Copiers) such as electrophotographic multifunction peripherals, facsimile machines, printers including laser printers, printing machines such as stencil printing machines, and multifunction peripherals formed of a combination of at least two of these apparatuses. In order to downsize these apparatuses, there is a tendency of downsizing transfer units for transferring and supplying a medium subject to imaging, which is a medium on which the image is formed or a recording medium in a sheet form (hereinafter also referred to as a “sheet”) from a sheet storage unit or a sheet stacking unit on which the sheets are stacked, to an image forming unit body.
As plural paper feed units and sheet transfer apparatuses which serve as a sheet feed unit provided in or connected to the image forming apparatus, for example, there is known an apparatus including a first transfer path through which a sheet is transferred, a second transfer path through which a sheet is transferred from an opposite side of the first transfer path, and a combined transfer path into which the first transfer path and the second transfer path merge (for example, see Patent Documents 1, 3, and 4). The first transfer path (hereinafter also called a first transfer channel) is, for example, generally provided in a sheet transfer apparatus in a plural-stage paper feed unit, which is also called a bank paper feed unit provided in an apparatus body. The second transfer path (hereinafter also called a second transfer channel) is, for example, provided on one side of the apparatus body. The second transfer path is generally provided or connected to a manual paper feed unit for supplying a relatively small number of sheets of various types in various sizes, or connected to a large amount paper feed unit or a large quantity paper feed unit for feeding a large number of sheets of, for example, thousands or more.
In image forming apparatuses including plural paper feed units and sheet transfer apparatuses with such a layout, the combined transfer path is generally provided for downsizing particularly a width direction of the apparatus body when a user faces and operates the apparatus in various ways, such as by supplying sheets. That is, the combined transfer path is normally provided to downsize a horizontal direction of the apparatus body when seen from a user facing the apparatus body. A technique to provide the combined transfer path is hereinafter called a “former technique”.
On the other hand, image forming apparatuses are generally compatible with various sheet sizes (hereinafter called “paper sizes” as an example) and sheet types (hereinafter called “paper types” as an example). In such image forming apparatuses, for example, paper in various sizes and types are stored in advance in a sheet storage unit. The paper is fed from the sheet storage unit selected by a user or the paper is automatically selected and fed by the image forming apparatus. In such a system, since the sheet storage unit occupies a large area in the image forming apparatus, the transfer unit is further required to be downsized.
In view of these, a transfer path provided between a sheet storage unit and an image forming unit body in the image forming apparatus has a transfer direction largely changed so as to reduce the occupying area, though depending on a positional relationship between the sheet storage unit and the image forming unit body. The transfer path is formed to have a curved part in order to change the transfer direction continuously and smoothly. A curvature radius of this curved part is set relatively small so that standard recording paper normally used in the image forming apparatus can be transferred.
As a sheet transfer apparatus in such an image forming apparatus, for example, there is a conventional technique disclosed in Patent Document 1. That is, as shown in FIGS. 6 and 7 of Patent Document 1, a paper feed tray is provided on a lower side of the image forming unit body. The paper feed tray serves as a sheet storage unit in which a predetermined number of sheets in predetermined sizes or types are stacked in corresponding stages. A sheet transfer apparatus capable of drawing one sheet in a substantially horizontal direction of the paper feed tray in the selected stage and feeding the sheet to the image forming unit body on an upper side is provided between the paper feed tray and the image forming unit body.
Hereinafter, description is made with reference to Patent Document 1. Reference numerals in each drawing of Patent Document 1 are described in parenthesis. A sheet (P) in a paper feed tray (1) is separated one by one by a known FRR separation method and transferred through a transfer path having a curved part which is formed of an upper guide board (8) and a lower guide board (7), and to an image forming unit body. The curved part is formed of a curve fixing guide member formed of the upper guide board (8) and the lower guide board (7). The sheet (P) passes through the curved part along the lower guide board (7). As the sheet (P) is transferred, the sheet (P) is pressed and adjusted in its transfer path by the upper guide board (8). The sheet (P) is transferred along a guide piece (6) capable of elastic deformation, which is located at an exit of the lower guide board (7), and reaches a pair of transfer rollers (5). Hereinafter, the upper guide board (8) and the lower guide board (7) are called the “curve fixing guide member”.
When a sheet (P) such as special paper having a high stiffness, including an envelope or recording paper such as thick paper is transferred in a sheet transfer apparatus having the aforementioned configuration, since a curvature radius of the curved part of the transfer path is small, resistance caused when the sheet (P) is bent and transferred along the curvature is much higher than resistance of a sheet such as normal paper for copying. Therefore, there is a problem in that the sheet (P) such as recording paper and special paper with high stiffness cannot be transferred and a paper jam or a transfer defect is caused.
This operation is described more specifically below. When a leading edge (leading edge side) of the sheet (P) in a transfer direction reaches the curve fixing guide member formed of the upper guide board (8) and the lower guide board (7), a front half part of the sheet (P) on the leading edge side is bent in a direction of the thickness by this curve fixing guide member. Therefore, when the highly stiff sheet (P) is transferred, the sheet (P) has a large force resisting the curve. This force increases resistance that prevents the transfer of the sheet (P). Therefore, when the leading edge of the highly stiff sheet (P) does not reach the pair of transfer rollers 5 on the downstream side and the sheet (P) is transferred by only a pair of rollers (2a and 2b) on the upstream side, and the sheet (P) is bent by the curve fixing guide member, a transfer force of only the pair of rollers (2a and 2b) is not enough to transfer the sheet (P) in the transfer direction against the resistance force of the bent sheet (P). As a result, transfer defects may be caused such as skewing of the highly stiff sheet (P), in which a center line of the sheet (P) is not aligned with the center line of the transfer path. Moreover, a paper jam is easily caused, in which the highly stiff sheet (P) is stuck within the curve fixing guide member and seized.
In view of this, Patent Document 1 discloses a paper feed apparatus in which a sheet transferred by a first transfer unit is transferred to a second transfer unit located on a downstream side of a transfer direction and substantially vertically above the first transfer unit. A pair of straight guiding members is provided between the first transfer unit and the second transfer unit, by which a sheet is guided and transferred. In this paper feed apparatus, the guiding members are not curved but formed straight, therefore, a transfer load can be suppressed low. That is, since a rapid rise of the transfer load can be prevented, transfer defects such as a paper jam and skewing of paper can be prevented.
According to this paper feed apparatus, in other words, the transferred sheet is not bent only at one point by the curve guiding member but two points in the vicinity of front and rear edges of the straight guiding members. Moreover, by providing the straight guiding members to be inclined at a substantially medium angle, curves caused by the two points are made substantially equal to each other. In this manner, a rapid rise of a transfer load can be suppressed when the sheet is transferred. That is, to change the transfer direction of the sheet, the sheet is curved at two points: a point where the sheet is sent from the pair of rollers on the upstream side to the straight guiding members and a point where the sheet is sent from the straight guiding members to the pair of rollers on the downstream side. Therefore, at least the curvature of each point can be relatively small. In addition, the resistance caused by the curve at each point can be suppressed low. As a result, a rapid rise of the transfer load can be avoided.
There is known a paper feed apparatus (for example, see Patent Document 2) including first and second transfer units configured similarly to Patent Document 1; and an inversion guiding member serving as a sloped surface leading to the second transfer unit, which is provided between the first and second transfer units. This inversion guiding member is configured movable toward the second transfer unit (for example, see Patent Document 2).
According to this paper feed apparatus, when a rear edge of paper contacts the inversion guiding member, the inversion guiding member is displaced in a direction that is generally the same as a direction that the rear edge contacts the inversion guiding member. By this displacement, a shock caused by the contact of the rear edge of the paper can be absorbed. As a result, a noise made by the flipping of the paper can be reduced.
Moreover, there is known a sheet feeding apparatus (for example, see Patent Document 3) including plural sheet storage units which store sheets, and a transfer path and a sheet feeding unit provided for each sheet storage unit. Ends of these transfer paths merge into one common transfer path. In at least the transfer path provided for the sheet storage unit which stores highly stiff sheets, a curvature radius of a first curved part formed at an end of the transfer path, which is to be merged to the common transfer path, is larger than a curvature radius of another curved part of another transfer path, which is combined to the common transfer path.
According to this sheet feeding apparatus, when a highly stiff sheet is transferred through the first curved part with the large curvature radius on the transfer path, the highly stiff sheet is not curved as much as a normal sheet. The highly stiff sheet is curved moderately enough as compared to the normal sheet when transferred. Therefore, resistance caused when transferring the highly stiff sheet can be reduced and the sheet can reach the common transfer path without causing a paper jam or a transfer delay.
Further, there is known a sheet inverting unit (for example, see Patent Document 4) provided in an image forming apparatus. The sheet inverting unit includes a pair of inverting rollers and an inversion transfer path for transferring and guiding a sheet sent by the pair of inverting rollers. The inversion transfer path has a direction changing member for changing a transfer direction of the sheet. By providing rotatable rollers inside the direction changing member in a vertical direction to the sheet transfer direction, the sheet sent to the inversion transfer path is contacted by the rollers and transferred.
According to this sheet inverting unit, an inside surface of the sheet necessarily contacts the rollers in the direction changing member. Moreover, since these rollers rotate following the transfer of the sheet, transfer resistance can be reduced compared to a conventional guiding board. That is, a transfer direction of the sheet can be changed in the direction changing member, without generating friction resistance between a fixed guiding member and a moving sheet.
Patent Documents 1 to 4 are hereinafter described as “latter techniques”.
The former technique, however, has a problem in that various types of sheets in various sizes cannot be transferred with stable transfer quality from the first and/or the second transfer path while realizing downsizement and compactness of a width of the apparatus, which has been demanded these years in particular.
The latter techniques, on the other hand, have the following defects. That is, since the sheet transfer apparatus disclosed in Patent Document 1 has a configuration having a fixed member provided for guiding a transferred sheet, there is always a difference in speed between the transferred sheet as a moving object and the fixed guiding member. Regardless of the shape or position of the guiding member, there is always resistance to disturb the transfer of the sheet between the sheet and the guiding member, which becomes a transfer load.
That is, by the conventional configuration, a sufficient effect to avoid the transfer defect or paper jam cannot be provided. Even if a rapid rise of the transfer load can be suppressed by the straight guiding member, the transfer load is generated in any way. When transferring highly stiff paper (sheet) such as thick paper and an envelope, in particular, the transfer defect, paper jam, and flipping noise of a rear edge of the paper are notably generated.
In the configuration having the inversion guiding member, which is disclosed in Patent Document 2, although the guiding member is displaceable in a direction in which the rear edge of the paper contacts, the inversion guiding member is a fixed guiding member to change the direction of the paper. Moreover, when the inversion guiding member guides the paper by changing the direction of the paper, a relative difference in speed between the paper and the inversion guiding member, which becomes a transfer load, is not eliminated. When highly stiff paper (sheet) such as thick paper and an envelope is transferred, in particular, the transfer defect, paper jam, and flipping noise of the rear edge of the paper are notably generated.
Further, by the configuration having the transfer path with a large curvature radius as in the technique disclosed in Patent Document 3, a sheet transferred on this transfer path is moderately curved. Although transfer resistance applied from the transfer path to the sheet is reduced, the transfer load is similarly generated more or less. When highly stiff paper (sheet) such as thick paper and an envelope is transferred, in particular, the transfer defect and paper jam are notably generated.
In the configuration having a movable member such as rollers in a predetermined position of inside the transfer path of the direction changing member as in the technique as disclosed in Patent Document 4, friction resistance between the sheet and the transfer path can be effectively reduced when an intermediate part between leading and rear edges of the sheet is supported by the rollers of inside. However, there is no countermeasure for a transfer load generated before and after the aforementioned state, that is when the sheet contacts outer sides of the transfer path of the direction changing member. Moreover, there is no particular description about the movement of the leading and rear edges of the sheet in the transfer process. When highly stiff paper (sheet) such as thick paper and an envelope is transferred, in particular, the transfer defect and paper jam are notably generated.
In view of this, the applicant has suggested a sheet transfer apparatus which can solve the defects of the latter techniques, an image forming apparatus having the sheet transfer device, and the like in Japanese Patent Application No. 2006-214779 (hereinafter called “a related Japanese application 1”) filed on Aug. 7, 2006, and the like. The related Japanese application 1 includes a movement guiding unit (specifically a belt transfer unit) arranged in a direction of an outer surface of a sheet transfer path formed between first and second transfer paths, for moving and guiding a sheet to the second transfer unit. According to the related Japanese application 1 and the like, the sheet transfer apparatus which is compact, occupies less space, has a simple configuration at lower cost, and is highly compatible with various sheet types (paper types), an image reading apparatus having the sheet transfer apparatus, and an image forming apparatus having the sheet transfer apparatus and/or the image reading apparatus are provided.
Moreover, in applying related Japanese application 1 and the like to the sheet transfer apparatus and the image forming apparatus which have the combined transfer path to put these apparatuses into a practical use, the present applicant has applied Japanese Patent Application No. 2007-46215 filed on Feb. 26, 2007 (hereinafter called “a related Japanese application 2”). According to the related Japanese application 2, there are provided a sheet transfer apparatus, an image forming apparatus, and the like, in which various types of sheets in various sizes can be transferred from the first and/or second transfer path while downsizing the apparatus compared to the conventional apparatus, or in which various types of sheets can be transferred with stable transfer quality by forming one of the first and second transfer paths to have a large curvature radius with a similar apparatus width to the conventional apparatus. According to the related Japanese application 2, the sheet transfer apparatus includes a first transfer path through which a sheet is transferred, a second transfer path through which the sheet is transferred from an opposite side of the first transfer path, a combined transfer path into which the first and second transfer paths merge, and a belt transfer unit provided as an outer surface of the combined transfer path when seen from the first transfer path and an inner surface of the combined transfer path when seen from the second transfer path, that is on the second transfer path side.
According to the related Japanese application 2, various types of sheets in various sizes can be transferred from both of the first and second transfer paths while downsizing the apparatus compared to the conventional apparatus, or various types of sheets can be transferred with stable transfer quality with a similar apparatus width to the conventional apparatus and the curvature radius of one of the first and second transfer paths set large. Accordingly, design freedom can be expanded.
However, while performing tests to apply related Japanese application 2 to the sheet transfer apparatus having the combined transfer path and the image forming apparatus to put these apparatuses into a practical use, it was found that some improvements are required. Specifically, though described with reference to FIG. 10 below, on the downstream side of the first guiding member provided at a position where the first and second transfer paths meet and configured to guide the sheet transferred from the first and second transfer paths to the combined transfer path, opposite end portions of a leading edge of a relatively stiff sheet such as thick paper transferred from the second transfer path, in particular, generates waviness or sagging at both ends of the sheet width direction of the belt transfer unit outside a nip part of the sheet. Because of this, the sheet cannot be normally transferred and a paper jam and a transfer defect are caused. As a result, there is a problem in that a stable transfer operation cannot be performed.
[Patent Document 1] Japanese Patent Application Publication No. 2004-338923 (pages 1 to 3 and FIGS. 1 to 7)
[Patent Document 2] Japanese Patent Application Publication No. 2005-89008 (pages 2 and 3 and FIGS. 4 and 5)
[Patent Document 3] Japanese Patent Application Publication No. 10-129883 (pages 1 and 2 and FIG. 1)
[Patent Document 4] Japanese Patent Application Publication No. 2005-1771 (pages 1 and 2 and FIG. 1)